This invention relates to a method for sizing a mask, such as a photolithographic mask, for alignment to a substrate. More particularly, this invention relates to such method wherein the mask is mounted in a frame comprising a side that is individually heated to stretch the mask and thereby achieve accurate dimensions therein.
In the manufacturer of microelectronic components, such as integrated circuit die or printed circuit boards, it is common practice to utilize a mask to limit processing to selected regions. By way of a common example, a photolithographic mask is employed to selectively expose and develop a photoresist layer. The photolithographic mask is formed of a thin polymeric film and is affixed to a glass plate. Precise alignment of the mask and the workpiece is required, particularly in forming fine features having dimensions of a hundred microns or less. For this purpose, the mask typically comprises fiducials and is aligned so that the fiducials in the mask register with fiducials on the workpiece. In order to obtain precise registration, the dimensions between fiducials on the mask must precisely correspond to the dimensions between fiducials on the workpiece. Difficulty is experienced in forming the mask with such precise dimensions. Moreover, even though formed with precise dimensions, the polymeric film is susceptible to variations in the ambient conditions, including particularly temperature and humidity. Because of a microscopic precision, variations of one or two degrees Centigrade or three or less percent relative humidity are sufficient to significantly effect the dimensions of the mask. Still further, in processing a series of substrates, variations occur in the features between individual substrates, which requires compensation in order to achieve precise location of features subsequently formed on the workpiece. Therefore, there is a need for precisely adjusting the dimension of a mask after the mask is formed and while at the workstation to bring the dimensions of the mask into congruence with the substrate.